Olefin polymerization catalysts are of great use in industry. Hence, there is a growing interest in exploring new catalyst systems and efficient methods for manufacturing such catalysts. Catalysts for olefin polymerization are often based on metallocenes as catalyst precursors, which are typically activated either with the help of an alumoxane, or with an activator containing a non-coordinating anion.
A metallocene catalyst component often appears in two stereo-isomeric forms: a racemic form and a meso form. A stereospecific catalyst is generally used to prepare stereoregular polyolefins. The racemic form induces a reproducible orientation of incoming monomers when the catalyst component is used in an olefin polymerization reaction. This is desirable for producing an isotactic polyolefin. Efforts have been made either to avoid the production of the meso isomer or to separate the desirable racemic isomer from the meso isomer, but the separation step is costly and it has been observed that after purification the meso isomer is reintroduced in the system under the effect of light or heat. Hydrogenation of the catalyst component avoids the formation of the meso isomer and/or its “re-formation” under the effect of light or heat. As such, a hydrogenated metallocene catalyst component is favorable in olefin polymerization.
Synthesis of hydrogenated or partially hydrogenated metallocenes generally starts from the corresponding metallocenes having aromatic ligands. The metallocene is dissolved or suspended in dichloromethane and hydrogenated in the presence of platinum black or platinum dioxide under a high pressure of hydrogen. An alternative to the above synthesis can be hydrogenation of metal complexes, followed by reaction with cyclopentadiene. Examples include metallocenes possessing 4,5,6,7-tetrahydroindenyl groups that are widely used in preparation of stereoregular polyolefins, for example, cyclopentadienyl tetrahydroindenyl metal complexes obtained by hydrogenation of corresponding cyclopentadienyl indenyl metal complexes.
WO 2010/077163 relates to the synthesis of substituted tetrahydroindenyls and the use of the synthesized complexes in the homo- and co-polymerization of ethylene and α-olefins.
U.S. Pat. No. 6,541,584 provides a class of bridged bis(tetrahydroindenyl)metallocenes of Formula (I), wherein M is Zr or Hf; X are monoanionic sigma ligands; (ZR1i)j is a divalent group bridging the two tetrahydroindenyl residues; R2 and R3 are halogen, alkyl, cycloalkyl, aryl, alkylaryl, or arylalkyl radicals; p is 0-3; i is 1 or 2; j is 1-4; m is 1-2; and n is 0-8. Furthermore, catalyst systems for olefin polymerization containing them are described.
U.S. Pat. No. 5,883,275 discloses a process for the hydrogenation of metallocenes, which comprises treating at least one metallocene containing at least one double bond and/or at least one aromatic substituent in at least one nonhalogenated solvent with hydrogen in the presence of at least one hydrogenation catalyst.
In view of the above, it will be understood that there is a further need in the art for improved routes to prepare a hydrogenated metallocene catalyst for olefin polymerization, which catalyst can facilitate polymerization of olefins to high isotacticity.
The inventor has found that, starting from annulated cyclopentadienyl metal complexes of the type (J)pCpMXnLm (Cp=cyclopentadienyl), as defined below, corresponding hydrogenated metal complexes (JH)pCpMXnLm, as defined below, can be conveniently formed by hydrogenation, which can be subsequently converted to metallocene catalysts of the type Cp((JH)pCp)MX2, as defined below, for use in catalysis of olefin polymerization. In contrast with the commonly used synthesis of tetrahydroindenyl metal complexes starting with tetrahydroindenide compounds, which is very time-consuming (a six-step process) and low in yield, for example, the present invention can provide an easy and high-yield alternative for preparing tetrahydroindenyl metal compounds, which can be useful in efficient catalysts for olefin polymerization.
Examples of transformations of the coordinated cyclopentadienyl ligands of Group 4 metal complexes resulting in no modification of the nearest coordination polyhedron have been described, e.g., H/D exchange in η5-cyclopentadienyls (Larsonneur, A.-M.; Choukroun, R.; Jaud, J. Organometallics 1993, 12, 3216); Pd/C or PtO2 catalyzed hydrogenation of η5-indenyls giving η5-tetrahydroindenyls (Wild, F. R. W. P.; Zsolnai, L.; Huttner, G.; Brintzinger, H. H. J. Organomet. Chem. 1982, 232, 233. Schafer, A.; Karl, E.; Zsolani, L.; Huttner, G.; Brintzinger, H. H. J. Organomet. Chem. 1987, 328, 87. Bandy, J. A.; Green, M. L. H.; Gardiner, I. M.; Prout, K. J. Chem. Soc., Dalton Trans. 1991, 2207. Rheingold, A. L.; Robinson, N. P.; Whelan, J.; Bosnich, B. Organometallics 1992, 11, 1869. Hollis, T. K.; Rheingold, A. L.; Robinson, N. P.; Whelan, J.; Bosnich, B. Organometallics, 1992, 11, 2812); hydroboration of allyl- and vinyl-η5-cyclopentadienyl complexes (Erker, G.; Nolfe, R.; Aul, R.; Wilker, S.; Kruger, C.; Noe, R. J. Am. Chem. Soc. 1991, 113, 7594. Erker, G.; Aul, R. Chem. Ber. 1991, 124, 1301); intramolecular photochemical [2+2] cycloaddition of vinyl-η5-cyclopentadienyl complexes (Erker, G.; Wilker, S.; Kruger, C.; Nolte, M. Organometallics 1993, 12, 2140); Ru-catalyzed metathesis of bis(allyl-η5-cyclopentadienyl) zirconium and -hafnium dichlorides (Ogasawara, M.; Nagano, T.; Hayashi, T. J. Am. Chem. Soc., 2002, 124, 9068).